This invention relates to methods and apparatus for finishing the surfaces of commutators on armatures for electric motors or other dynamo-electric machines.
The condition of the finished surface of a dynamo-electric machine armature commutator is of considerable importance to the satisfactory operation of the machine. For example, in an electric motor which has a cylindrical commutator surface on its armature, perfect roundness and concentricity of the finished commutator surface helps ensure steady contact between the rotating commutator and the stationary brushes which bear on the commutator during operation of the motor. On the other hand, the surface of the commutator is preferably neither too smooth nor too rough. If the commutator surface is too smooth, the commutator will not cause the brushes to "run in" properly, which may cause undue current concentrations or arcing in the regions of contact between the brushes and the commutator. If the commutator surface is too rough, the brushes may wear too rapidly. Commutator surface conditions such as these become more important with increased motor speed, and there is growing interest in motors that operate at higher speeds.
There is also increasing interest in motor manufacturing equipment that can make motors more quickly. This means that the traditional quality control methods, which involve periodically testing completed motor parts, may not detect defects (e.g., due to worn or broken tooling, or tooling which is improperly or sub-optimally adjusted) early enough to prevent the production of large quantities of unacceptable parts.
A desired increase in manufacturing speed also means that many traditional manufacturing systems, which include process steps that limit the speed at which motors can be manufactured, must be revised. For example, traditional commutator turning operations require that commutators be turned to a predetermined diameter and then turned again to finish the surface of the commutator. This typically results in a substantial portion of at least some of the commutators being cut off (through the first turning operation). As such, the armatures must be formed from commutator bars that initially are artificially thick resulting in excessive supply costs for copper (a typical commutator material) which is not part of the finished product.
In view of the foregoing, it is an object of this invention to provide improved methods and apparatus for finishing commutator surfaces.
It is another object of this invention to provide commutator surface finishing methods and apparatus which do not require artificially thick commutator bars before commutator finishing.
It is a further object of this invention to provide commutator surface finishing methods and apparatus which reduce the time required to finish a commutator.
It is a more particular object of this invention to provide commutator surface finishing methods and apparatus which include more "in-line" monitoring of the condition of the commutator surface in order to detect possible defects more quickly and thereby prevent the production of large numbers of defective parts prior to defect detection.
It is still another more particular object of this invention to provide commutator surface finishing methods and apparatus in which "in-line" monitoring of the condition of the commutator surface is used for such purposes as detecting trends that may indicate that defective parts are about to be produced so that corrective action can be taken before such defective parts are actually produced.
It is yet another more particular object of this invention to provide commutator surface finishing methods and apparatus in which "in-line" monitoring of the characteristics of the commutator surface is used to provide early warning to the operator of a problem or an incipient problem and/or automatic adjustment of the commutator surface finishing apparatus to correct the problem or incipient problem.